Pyrolysis of secondary-butylbenzene derivatives



Patented Dec; 5, 1939 UNITEDSTATES PATENT OFFICE PYROLYSIS OF' SECONDABY-BUTYLBEN- ZENE DERIVATIVES Robert R. Dreisbach, Midland, Mich., assignor to The Dow Chemical Company, Midland, Mich, a corporation of Michigan No Drawing. Application November 12, 1937, Serial No. 174,221

9 Claims.

This invention concerns the pyrolysis of a henzene derivative having the general formula wherein X and Y each represent hydrogen, halo:

gen, or an alkyl radical and n and n are. integers butylbenzene has not previously been pyrolyzed 20 nor has the formation of an allyl benzene by pyrolysis of any alkyl benzene heretofore been' known.

I have now found that a secondary-butylbenzene compound having the above general formula may be pyrolyzed to obtain a vinyl aromatic compound and an allyl aromatic compound, and that the respective yields of these two types of products are at least partially dependent on the temperature at which the pyrolysis is carried out and may be controlled. More specifically I have discovered that secondary-butylbenzene may be pyrolyzed to produce styrene and allyl benzene and, other operating conditions being constant, that the yield of styrene increases and that allyl benzene decreases as the pyrolysis temperature is raised. I have further discovered that activated charcoal catalyzes the reaction for the formation of styrene and enables the latter to be produced in good yield at pyrolysis temperatures much lower than are required to obtain the same yield of styrene in the absence of such catalyst. The invention, then, consists in the method hereinafter fully disclosed and particularly pointed out in the claims.

The pyrolysis is carried out at temperatures above 450 C. by heating the butylbenzene compound and cooling it before excessive carbonization can occur. The period during which the compound may be maintained at a pyrolyzing temperature depends of course upon the maximum temperature employed and the particular compound-under treatment, but for any given compound the permissible period. of heating decreases as the pyrolysis temperature is raised. Theoretically, the pyrolysis could be carried out at very high temperatures, e. g. 1200 C., by employing a shock mode of heating wherein the compound would be heated and cooled almost instantaneously, but it is usually impractical to operate at temperatures above 950 C. It is inadvisable to heat the secondary-butyl compound at tgmneratures above 750 C. for more than 0.1 second, since otherwise carbonization and tar formation may occur to objectionable extent, but longer periods of heating may be em- 10 ployed and are usually required when operating at lower temperatures.

The pyrolysis may be carried out in any of the usual ways, e. g. by passing 'a secondary-butylbenzene compound alone or in admixture with a gaseous diluent such as steam or carbon dioxide through an externally heated tube or a bath of lead or other molten metal, but as hereinbefore stated care must be taken to heat and cool the I vapors with suflicient rapidity to avoid'excessive carbonization. In practice, the pyrolysis is preferably carried out according to the general methed for pyrolyzing alkylated aromatic hydrocarbons set forth in my co-pending application,

Serial No. 151,457, filed July 1, 1937, of which this application is a continuation-in-part. This preferred mode of operation, described below, permits the desired products to be formed in higher yield than I have found possible by the usual pyrolytic -methods, without appreciable carbonization or tarring of the reaction mixture.

A liquid or vaporized secondary-butylbenzene compound and superheated steam are passed continuously into admixture with one another, the steam being employed in the proportion and at the temperature required to attain the reaction temperature and furnish the heat of pyrolysis. Usually, between 7 and 10' parts by weight of steam superheated to a temperature between 600 and 1000 C. is used per part of the second- 40 ary-butylbenzene compound, but the steam may of course'be employed in other proportions and at other temperatures. The mixture is passed through the reaction tube at arate permitting substantial pyrolysis but sufiicient to prevent appreciable carbonization or tar formation. Ashereinbefore stated, this rate varies somewhat depending on the particular secondary-butyl compound under treatment and the temperature employed. In general, however, best results are 5 obtained when the rate is such that the vapors are maintained at a pyrolysis temperature of 450 C. for not more than 2 seconds, at 750 C. for not more than 0.1 second, and at 900 C. for not more than 0.03 second. The mixture issuing from the .gy-buwbenzenetube is cooled rapidly, e. g. by contact with water I components of the mixture. The 'organic'condensate is then distilled, preferably under vacuum, to separate the vinyland allyl-type products. Any unreacted secondary-butylbenzene compound recovered in the distillation is returned to the pyrolysis.

The following examples illustrate certain ways in which the principle of the invention has been applied, but are not to be construed as limiting the invention: Y

Example 1 One part by weight of vaporized secondary butylbenzene and about 8.5 parts of steam superheated .to about 880 C. were passed simultaneously into a reaction chamber to form a mixture having a temperature of about 550 C. The mixture passed through the reaction chamber and into suitable coolers and condensers at such rate as to be maintained at 550 C. or thereabout for only about 0.5 second. The so-treated mixture was cooled suificiently to condense the,aromatic components thereof. There was obtained 0.96 part by weight of" organic. condensate containing approximately 12.8 per cent by weight of allyl benzene and 87.2 per cent of unreacted second- Eazample 2 Secondary-butylbenzene was vaporized and passed into admixture with about 8.5 parts by weight of steam which had been superheated suiiiciently so that the mixture formed was of a temperature of about 725 C. The mixture was cooled to below700 C. within about 0.05 second after formation and the cooling was continued to condense the aromatic components of the mixture. The organic condensate was a clear brown- 1 ish liquid containing approximately 67.4 per cent by weight of unreacted secondary-buty'lbenzene, 22 percent of allyl benzene, 1.7 per cent of benzene, and less than 1 per cent of styrene.

Example 3 Secondary-butylbenzene was pyrolyzed at a temperature of about 730 C. by admixture withsuperheated steam, the procedure being similar to that described in Example 2, except that the pyrolysis mixture was passed, immediately after formation, through a bed of granular activated charcoal at such rate as to be contacted with the charcoal for approximately 0.08 second. The

vapors issuing from the charcoal were promptly 23 per cent of allyl benzene, and minor propor-.

cooled sufliciently to condense the aromatic products. The organic condensate contained approximately 33 per cent by weight of unreacted sec? ondary-butylbenzene,. 29.7 per cent of styrene,

tions of benzene and ethylbenzene.

. email A mixture of ortho-chloro-secondary-butylbenzene and meta-chloro-secondary-butylben-' zene was pyrolyzed at a temperature of about 550 C. by admixture with superheated steam, the

procedure in carrying out the pyrolysis and condensing the product being similar to that described in Example 1. The organic condensate was a slightly colored liquid containing about 79 per cent by weight of unreacted chloro-butylbenzenes, 8 per cent of orthoand meta-chloro- 2,1e2,s1s

allyl benzenes, and minor proportions of byproducts -such as chloro-isopropyl benzenes, chloro-styrenes, etc.

Example 5 A mixture of isomeric ethyl-secondary-.butyl-' benzenes was pyrolyzed at a temperature of about "80 C. by admixture with superheated steam and I the aromatic products were condensed, the procedure being similar to that set forth in Example 2. The liquid organic condensate contained approximately 10.2 per cent of unreacted ethylseoondary-butylbenzenes, 44.8 per cent of ethylallylbenzenes, 22.8 per cent of ethyl-vinylbenzenes, 6.2 percent of' styrene, and minor proportions of by-products such as diethylbenzene,

ethylbenzene, etc.

Other secondarybutylb'enzene compounds may be pyrolyzed in accordance with the invention to plicated secondary-butylbenzene compounds numerous by-products are frequently obtained. These by-products usually include styrene homologues and analogues useful in preparing synthetic resins.

The expression "allylbenzene compound as hereinafter employed refers generically to allyl benzene and certain derivatives thereof preparable by the pyrolysis of nuclear substituted secondary butyl benzenes wherein the nuclear substituents are halogen or lower alkyl groups.

Other modes of applying the principle of the invention may be employed instead of those explained, change being made as regards the method herein disclosed, provided the step or'steps stated by any of the following claims or theequivalent of such stated step or steps be employed.

I therefore particularly point out and distinctly claim as my invention:

1. The method which comprises pyrolyzing secondary-butylbenzene to obtain allyl benzene.

, 2. In a method for producing allyl benzene, the step of pyrolyzing secondary-butylbenzene at a temperature not exceeding 800 C.

3. In a method for producing allyl benzene, the step of pyrolyzing secondary-butylbenzene at a temperature not exceeding 800 C. by admixing the secondary-butylbenzene with steam super-,

ondary-butylbenzene in the presence of activated rolysis temperature, passing the freshly formed pyrolysis mixture into contact with activated 1e I charcoal and promptly thereafter cooling the mixture.

'7. In a method for making an allylbenzene compound the step which consists in pyroiyzing a 5 compoundhaving the general formula:

' X, CHa

sf :H-cHrcH= Y, V 10 wherein X and Y each represents a substituent selected from the group consisting of hydrogen,

halogen and lower alkyl substituents and n and 11. are integers having a sum not exceeding 5.

8. In a method for making an allylbenzene 15 compound the steps which consist in pyrolyzing a compound having the general formula:

wherein X and Y each represents a substituent selected from the group consisting of hydrogen, halogen and lower alkyl substituents, and n and n are integers having a sum not exceeding 5, by admixing said compound with steam superheated sufliciently' to attain the pyrolysis temperaturewherein X and Y each represents a. substituent selected from the group consisting of hydrogen, halogen and lower alkyl substituents and n and n are integers having a sum not exceeding 5, by passing the compound into admixture. with a curent of steam superheated 'suflicient'ly to attain f .ne pyrolysis temperature, passing the freshly ormedpyrolysis mixture into contact with ac- .ivate'd charcoal, and promptly thereafter cooling the mixture.

ROBERT R. DREISBACH. 

